The invention relates to an "auto shut-off" apparatus for a cassette tape recorder, and more particularly, to such apparatus in which the detection of a tape end being reached during a tape rewind mode unlocks a tape rewind member of the tape recorder to thereby deactuate the recorder operation automatically and to return the tape rewind member to its initial position.
A variety of "auto shut-off" apparatus are proposed and known for a cassette tape recorder for the purpose of automatically interrupting the recorder operation and for returning various operating members to their initial positions in response to the detection of a terminal end of a running tape being reached during a record or a playback mode of the tape recorder. Specifically, a conductive foil may be applied to a terminal end of a magnetic tape so as to be electrically detected to activate a stopping device. Alternatively, a terminal end of the tape may be formed with a portion of different optical reflectivity and transmittance from those of a magnetic surface, so that such portion may be optically detected to activate a stopping device. As a further alternative, a tape tension sensor applied to a guide roller for the magnetic tape may be utilized to mechanically detect a change in the tension as a tape end is reached, thereby activating a stopping device.
However, with a tape cassette, the containment of a magnetic tape within a cassette makes it very difficult and expensive to apply a suitable detectable portion to or otherwise machine the tape end. In this respect, the use of stop means which is commonly referred to as a "mechanical stop" utilizing the tape tension will be more advantageous. Since a cassette tape has its one end secured to one of the tape hubs and its other end secured to the other tape hub, the rotation of the tape hubs will be interrupted when a tape end is reached on the supply hub. As a consequence, a tape drive shaft which engages the supply hub will slip relative to the hub, experiencing an increased load. This can be detected to activate a mechanical stop.
However, a mechanical stop which accurately detects a change in the load on the tape drive shaft is very complex and occupies an increased amount of space within the recorder. While such a mechanical stop may be assembled into a tape recorder which is adapted to use a tape cassette of a size commonly referred to as a compact cassette, it cannot be incorporated into a tape recorder of a miniature size which can be received into the pocket of a suit or shirt and which is adapted for use with a micro-cassette. Thus it will be seen that a miniature tape recorder using a micro-cassette cannot utilize the mechanism which detects a change in the load on the tape drive shaft due to the limited space available.
In both the micro-cassette and compact cassette, the tape hubs on which the magnetic tape is received is mounted with respect to the cassette body so that they are slightly movable or capable of "rattling" with respect to the cassette body in order to facilitate the fitting of the tape hubs onto the associated shafts. In consideration of this fact, a tape supply shaft which engages one of the tape hubs may be disposed in a displaceable manner so that when a tape end is reached on the supply hub, it is possible to provide a movement of the supply hub together with the supply shaft within the limited extent permitted by the rattling clearance of the tape hub. Such movement of the tape supply shaft may be detected to unlock an operating member which maintains the tape recorder in operation, thus automatically stopping the tape recorder. The present applicant has previously proposed an auto shut-off apparatus for a tape recorder which detects such movement of the tape supply shaft when a tape end is reached on the supply shaft during the transport of the tape in the forward direction, namely, during a record or playback mode.
In order to permit the use of similar means to provide an auto shut-off function of the tape recorder during a tape rewind mode, namely, during the transport of the tape in the opposite direction, a tape take-up shaft, that is, a shaft associated with a tape hub on which the tape is taken up during the tape transport in the forward direction, must also be supported in a displaceable manner. However, the displaceable arrangement of both the tape take-up and the tape supply shaft results in the loss of a stationary shaft which provides a reference to the movement, whereby the auto shut-off mechanism will become very complex and exhibit an unstable operation.
In a tape recorder, means for transmitting a rotating drive to a tape take-up shaft usually comprises a gear train or a transmission belt. Where a gear train is used, the rotating drive is transmitted to the tape take-up shaft from a drive gear through a plurality of intermediate gears. However, an increase in the number of transmission gears may give rise to the instability of rotation of the tape take-up shaft as a result of an increased error in the transmission of the rotating power due to a meshing misalignment between the gears. It will be understood that during the rewind mode, it is only necessary that the tape be driven in the opposite direction, and the tape transport in this direction need not consider the tape running speed or the speed of rotation of the rewind shaft, so that an increase in the number of gears does not present a problem. However, when the tape runs in the forward direction as in the record or playback mode, it is desirable that the tape take-up shaft exhibits a stabilized rotation so that it is capable of receiving the tape as it is forwardly fed at a uniform rate by the cooperation of a capstan and a pinch roller. Thus, it is undesirable that the system which drives the tape in the forward direction involves an increased number of gears.